In All-Star Comics #50 (October 1949), it is established for the first time that the members of the Justice Society of America know each other’s secret identities. Jay Garrick (The Flash) and his college classmates had written down their ambitions a decade before with their professor, and one of the classmates had decided to become “the most unique and daring criminal of all time”, Mr. Alpha.
Check out The Atom in this panel. The artist was Arthur F. Peddy, who at the time, either didn’t understand the concept of perspective or the fact that The Atom is supposed to be short in stature.